1. Field of the Invention
The present invention relates to methods and circuit configuration for driving a liquid crystal display panels of direct drive type.
2. Description of the Related Art
In driving methods of liquid crystal display devices, there are two major categories, i.e. a direct drive matrix type and an active matrix type. The active matrix type experiences difficulties in its production because active elements are required on every picture element at intersections of the matrix. Therefore, the direct drive matrix type has been widely employed for display panels having a large number of the picture elements.
It is widely known that in the liquid crystal display panel of the direct drive matrix, when data pulse voltages are applied onto selected data electrodes an undesirable spike voltage is induced on the unselected scan electrodes facing the data electrodes, through electrostatic capacitances of liquid crystal cells (referred to hereinafter as cells) connected to the data electrodes. The spike voltage is caused by differentiation of the change in the applied data pulse voltages by the cell capacitances. Optical transparency of each cell corresponds to an effective value, i.e. a square root of sum of squares of applied cell voltages for the voltage application period. Thus induced spike voltages on the unselected scan electrodes cause a cross-talk, i.e. non-uniformity, to develop on the display panel. Recent trend of increase in electrodes quantity on a larger panel causes not only an increase in electrical resistance of transparent electrodes but also a decrease in difference of the applied cell voltage to select an ON-STATE of the cell, where the cell is most transparent by an application of cell voltages, from a voltage to select an OFF-STATE, where the cell is least transparent by the least application of the cell voltages. Therefore, the cross-talk has been becoming more and more serious problem.
In order to eliminate the effect of such undesirably induced spike voltages, some methods have been proposed as described below. In Japanese un-examined patent publication Sho 63-240528, there is disclosed an idea that a compensation voltage is applied to unselected electrodes. However, none of its practical means is disclosed therein. In Japanese un-examined patent publication Sho 63-220228, there is disclosed a method that a voltage corresponding to the display data on a selected scan electrode is fed back to unselected scan electrodes. However, in these methods, it is impossible to compensate a cross-talk on the display which is caused from a change in the quantity of ON-STATE cells when the scan goes to a presently selected scan electrode from the just previously selected scan electrode.